WHAT IS IT?
A chat room is an online forum where people can chat online (talk by broadcasting messages to people on the same forum in real time). Sometimes these venues are moderated either by limiting who is allowed to speak (not common), or by having moderation volunteers patrol the venue watching for disruptive or otherwise undesirable behavior.
Chat systems come in a variety of flavors ranging from text only messaging systems to fully immersive 3D environments. By far the most common form in recent times is instant messaging (ICQ, AIM, MSN, Jabber, etc). Some would argue that these are not truly chat rooms as they are characterized by being one on one conversations with people in a users "buddy list". However as the popular media has confused the issue, this brief description is included here. Recently these systems have started to incorporate the ability to chat with multiple people simultaneously, but these are still conversations restricted to the users budylist, not a cocktail/block party style venue as true chat rooms are.
Chat-rooms are often confused (especially by the popular media) with discussion groups, which are similar but do not take place in real time and are usually run over the internet.
The oldest form of true chat rooms are the text-based variety. The most popular of this kind of chat room is Internet Relay Chat (or IRC). However, there are also talkers, bulletin board systems, and havens. The popularity of many these kinds of chat rooms have waned over the years, but IRC's popularity still remains strong.
At the next level are the 2D visual chat rooms. These are characterized by using a graphic representation of the user (avatar) that can be moved about a graphic background of the "room". (Two examples of this type of chat room are The Palace and more recently The Manor.) These environments are capable of incorporating elements such as games and educational material most often developed by individual site owners, who have a more in depth knowledge of the system. Some visual chat rooms also incorporate audio and video communications, so that users can see and hear each other, this is particularly popular with those keeping in touch with far-flung family members.
Finally, there are the 3D chat rooms. These are similar to the 2D variety except that they utilize 3D graphics. This allows a user a more realistic interaction with the environment. The most popular environments allow users to create or "build" their own spaces. However, some find these types of environments cumbersome to use and actually impede chatting.*